The invention relates to an apparatus and a method for checking value documents, in particular bank notes, as well as to a value document processing apparatus which has the apparatus for checking value documents.
In bank note processing systems properties of bank notes, such as e.g. printed image, face value, authenticity and soiling are ascertained, by physical properties of the bank notes being captured by means of sensors and the sensor data generated hereby being evaluated by means of algorithms.
From U.S. Pat. No. 5,468,971 it is known to capture a transmission image of a security thread located on a bank note and to subject it to character recognition for ascertaining the characters incorporated in the security thread. With the help of the security thread's inscription ascertained in this manner the denomination of the respective bank note is ascertained.
The known method presupposes, in particular with the check of security elements having a very small inscription, so-called microwriting, a very high resolving power of the respective image sensors as well as of the associated optics, so that a reliable character recognition can be guaranteed.